Sound apparatus for producing and receiving sound waves



Jan. 3, 1928. 1,655,267

W. HAHNEMANN ET AL SOUND APPARATUS FOR PRODUCING AND RECEIVING SOUNDWAVES Filed Aug. 7, 1925 In venrdro Wa/fer Habnemana fie/hrx-b Heel?! WW Alfarn 5 Patented Jan. 3, 1928.

UNITED STATES PATENT oF 1,655,267 IHCE.

WALTER HAHNEMANN, OF KITZEBERG, NEAR KIEIVI, AND HEIKBICH HECHT, OFKLEL, GERMANY, ASSIGNORS TQslGNALGEsELLSCHAFT MIT BESCHRANKTER EAFTUNG,

OF KIEL, GERMANY, A FIRM.

SOUND APPARATUS FOR PRODUCING AND RECEIVING" SOUND WAVES.

Application filed August 7, 1925, Seria1 No. 48,822, and in GermanyAugust 11, 1924.

i The invention reters to apparatus for the production and reception ofsound waves and moregenerally for the purpose to transfer vibratorymechanical energy from or to 5 the sound propagating medium and totransform mechanical vibratory energy into electrical vibratory energyand vice versa.

It is the problem of the invention toproduce devices of the kind abovespecified which are adapted to produce and to reproduce sounds of a verybroad range of fre- .quencies with, as far as possible, equal efiiciencyat all frequencies and with a high degree of efiiciency, andparticularly to avold distortion.

A further object vof the invention is to transfer energy with goodefiiciency between ifi'erent vibratory structures forming a part of thedevice, for instance between a diaphra'gm and a' detector (microphone orthe like). It is also the object of the invention to produce a devicefor the reception and reproduction of noises, for instance nolses inwater originating from the rotation of ships 4* propellers, and also adevice for the reception and reproduction of music and speech.

These several objects areaccomplished by coupling a plurality 'ofequally tuned mechanical vibratory structures, forming e16:

ments of the apparatus described, in such a manner that the resonancecrests in the resonance curve of the coupled structures of the apparatusare substantially evenly dis tributed over the' desired range offrequencies and that the ordinates of this curve between the resonancecrests do not sink below an undesired level, for instance below 30% ofthe ordinate of the neighboring resonance crests. Another feature of 40the invention consists in providingat least three vibratory structurescoupled in the manner above described. A further feature of theinvention consists in inserting a series of such coupled structuresbetween the sound emitting and receiving element (diaphragm) and theenergy converting means (detector, microphone) of the apparatus. Anotherfeature of the invention is that the intermediate structures are coupledwith one ani other in series; that is, that each structure is coupledwith the oneS adjacent to it and with no others.

These particular features of the invention and others may be seen moreclearly from Figure 1 shows diagrammatically the structure of Figure 1.

Figure 1 shows a resonance curve such as might be expected from astructure such as shown in Figure 1.

Figure 2 shows a further modification of the invention with a series ofcoupled resonators, and

Figure 3 shows a modification having a combined system composed ofcoupled resonators and diaphragms.

In, the art of communication or the like, in many cases it is desirableto operate over a very broadrange of fr uencies with one and the sameapparatus, either for the production and reception of sound waves, orfor other purposes wherever mechanical or electrical vibrations have tobe transferred or 'tran formed. Special examples of this kind are thefollowing:

In submarine signaling'it is often necessary to have'submarine soundtransmitters which are particularly adapted to receive water noises.While transmitters for signals covering a very small range offrequencies with high efiiciency are known, real satisfactory solutionsof the problem of transmission of noises do not exist, i. e. there aretransmitters today which' are capable of picking up and transferringsound over a small range of frequencies, as for instance over a range of10% to 20%, of the vibrations in the vicinity of the natural frequency aof the transmitter, but transmitters have not been designed to operatesuccessfully over a greater range of frequencies as. for instance oneoctave or more or from 500 to 1000 cycles.

It is also advantageous to provide a telephone for the reception of suchnoises efliciently and without distortion. Telephones possessing goodreceptive properties for single tones and frequencies are known, but theworking range over. varying frequencies with good efliciency islimltedto 20%- 3 0% of their resonance frequency (i. e. for instance from 900to 1200 cycles). Naturally these telephones are not satisfactory for thereception and transformation of electrical 5 fluctuations produced bywater noises transmitted from submarine sound receivers where a highefficiency over a broad range of frequencies is desired. This invention1s applicable therefore for the development of telephones capable ofoperating over a broad range of frequencies, for exampleover arange'ofone octave. Besides it is very desirable to produce telephonesof a high 'efli-' ciency for a broader range of frequencies,

5 especially for the pu-rposeof transforming speech vibrations, in whichcase it is desirable for avoiding distortlon to have a uniformefficiency over a number of octaves, if

possibleeven more than five octaves.

What has been said'above applies to loud speakers also. Apparatus ofthis kind has been developed recently which has a good efiiciency for adefinite range of frequencies, but even in this case .this range offrequencies was limited from about to of the middle frequency for whichthe devices were designed. It has been proposed to employ a number ofdevices of this kind operating to get-her, each of them being tuned to adiiferent range of frequencies so that the whole range of frequencies tobe transmitted is covered with equallyetficient devices. However, as thehuman speech contains frequen-' cies ranging over many octaves (at leastfive '5 to six) a very great number of such individual deviceswould'have'to be applied for -covering this whole range wlth a"sat1sfactory degree of eificiency. As it is desirable to dispense with agreater number of devices andto use as few as possible, preferably onlyone, this invention is particularly useful in this respect. i Theinvention is based 'upon gouphng a plurality of vibratory structures(three or more) with one another. The invention consists in adjusting insuch devices with relation to one another the dan'iping and the degreeofcoupling so that the resonance crests in the resonance curve of thecoupled system are evenly distributed over the range of frequencies tobe transinittedand that tl1c emitted or received energyat allfrequencies of this range is a substantial per cent of the maximumenergy at the points of thp resonance crests themselves. The evendistribution of the resonance crests is obtained ac- The followingdiscussion may elucidate coupling particu'l'arlylmve to be considered.-

If energy travels through a series of coupled systems a resonancediagram results with a plurality of. resonance points. If theefiiciencyof the transfer is to be made satisfactory'the individual structuresshould be tuned to the same natural frequency. The

resonance crests mentioned above in the coupling curve are under suchconditions positioned a distance from one another depending upon thedegree of coupling between the r individual structures. Broad curves areobtained by coupling the structures closely, each structure forming onecrest. Where many structures are coupled.

together the resonance curve hasa number of peaks equal to the number ofstructures, which peaks become broader the greater the number ofstructurescoupled togethen As the theory shows for a given naturalfrequency of the structures-the resonance crests cannot move farthertowards the higher frequency than to one and a half times the naturalfrequency, while towards the lower frequencies crests can exist until tothe lowest frequencies. One of the main features of the invention isthat in all cases the number of the structures coupled with one anotherand the degree of coupling between them is so adjusted that the desiredrange of frequencies is satisfactorily covered. .lVhere ,the-

structures havefslight damping the peaks of the resonant curves aresharp and the amplitudes on both sides of the peaks fall oil veryrapidly for changing frequencies. To

1 maintain therefore great amplitudes between peaks of the resonancecurve it is .necessary to have the peaks close to each other. Thus agreat number of resonant structures are necessary toprovide a. goodefliciency "at all points. The damping itself may be caused by radiationof energy or by wasting of. energy. In the mostcnses besides the desiredbroadresonance curve an initial vibratory structure is already provided,for

. instance in the case of a subn'iarine sound receiver the diaphragmtaking up the energ from the water and also the final vibratorystructure, the particular detector (microphone, electroi'nagnet or thelike). For these elements generally defined vibratory dimensiohs aregiven, especially the'value of the masses and the elasticity of theelastic members carrying the masses, with regard to the desiredproperties of the apparatus. a submari'nesound receiver with relativelylarge damping, generally a relatively large area of the diaphragm isnecessary, and consequently a relatively large mass and high For elasticforce of the carrying member, while for detectors, especially for. thenormal microphone with carbon grantiles, the mass apparently'may be verymuch smaller than the mass of a large receiving diaphragm. It may easilybe understood that it is extreme- 1y difficult to couple two suchstructures tlghtly together where there are entirely dif-' their massand elasticity, a tight coupling between these structures may beobtained. This way consists in inserting between the initial structureand the final structure a sufficient number of intermediate vibratorystructures which increase in number inversely as the masses decrease.If, for instance, the ratio of the masses of the initial structure andthe final structure is 1:100, a casein which for coupling by masses thegreatestpossible degree of coupling is by inserting only two additionalintermediate structures the individual ratio of masses betweenneighboring structures may be lowered to 1:5, the coupling beingenhanced in this way from 10% in the before mentioned case to and theresonance diagram being broadened accordingly. A further broadening ofthis diagram arises from the fact that, instead of two crests with 10%distance, now four crests with about i0% distance from one anotherexist. In this way by the means of the invention i. e. by theinterconnection of a plurality of conveniently coupled structures inthis case not only a broad resonance diagrain but also the best transferof energy between the initial structure (diaphragm with great radiationdamping) and the final structure (microphone of high sen'sitivenessi. c.with small mass) is obtained.

To explain this feature a little more fully, suppose that the initialstructure receiving the sound weighs 100 and the final structure used totransform the sound to electric oscillation weighs 1, both beingmeasured in the same units. 'These two structures may be coupled througha mass structure weighing 10. The result would be a coupling of a ratherloose nature. Suppose, however, there were inserted rstructures steppingdown from the 100 weight to the 1 in the ratio of 5 or approximatelythat, then the coupling would be closer and in addition there would alsobe a broadening and flattening of the resonance curve tending to producea system capable of, responding over a considerable range of frequency.

In the drawing in which some practical.

examples. of the invention are shown, Figure 1 represents a submarinesound transmitter and receiver, the initial structure of which Is adiaphragm a and the final structure of which is a detector d,-in thiscase an electromagnetic detector. Diaphragm and detector are coupledwith one another by two addi-- tional vibratory structures 6 and a. Eachtwo neighboring structures comprise a, common mass so'that the massesand elastic members are distributed to the structures as follows:

Structure a: masses 1 and 3, elastic mem her 2.

Structure 6: masses 3 and 5, elastic member 4.

Structure 0: masses 5 and 7 elastic 1118111. her 6.

b StSructure d: masses 7 and 9, elastic mem- These structures above areshown analytically'in Figure 1". Themass 1 is coupled to the mass 5 bymeans of the coupling mass 3, while 5 is coupled to 9 by means of themass 7. As is shown there are really four oscillatory structures, sinceall but the outer masses serve as mass elements of two vibratorystructures.

s has been stated above each of these oscillatory structures are tunedto the same frequency, each is similar to the other. In F igure 1 itwill benoted that the resonance curve of each individual structure a, b,c. d, is illustrated as being the same.

These oscillatory structures are combined together closely coupled sothat a considerabl-e amount of energy may be transferred from one to theother. They are combined together by so arranging them in order that themasses are arranged in steps according to their effective magnitude. Inthis way the coupling becomes very closeand a broad resonance results.The peaks which formerly came together are now separated even though theindividual structures have the "same natural frequency.

The result is that a structure is produced.

which is substantially equally responsive over a large range offrequencies. As will be noted the peaks of the structures of Hillsmaller weights go towards the higher end of the range while the heavierstructures descend below their natural frequency.

The cui've of Figure 1 having the four peaks is the resonance curve ofthe coupled structure. A loud speaker or the like having a resonancecurve-of this nature will resfiond equally well to the low vibrations asto the high ones.- In this case it is not really a question ofinterposing intermediate structures for the transfer of energy from them1- tiaLto the final structure but the evolution of a coupled tunedresonant structure which is'capable of responding tosounds of allfrequencies. -7

the vibrations, and others responding for In the actual combination allthe structures cooperate together, some responding and taking up theburden of operation when their particular structure is most affected bysounds of other frequencies. The idea is to have the sum total ofresponses 'of all structures about the same at all frequencies. Byclosely coupling these oscillatory structures together the oscillatoryenergy is easily transferred from one vibratory structure to the otherso that the one which should respond most has the energy andis capableof doing its part inthe whole'operation.

Mass 1 is the outer casing of the appara-,

tus, masses 3, 5 and .7 are metal casings carrying the elastic members4, 6 and 8 respectively. All elastic members in the example of Figure 1are diaphragms. They may be replaced by other elastic bodies, as rods,strips or the like. The final structure is i more clearly indicated byFigure 1. It con- The problem in this case is to have the diaphragmcooperate with the telephone and the ear canal efliciently over abroad'range of frequencies. According to this modifica tion a number ofcoupled resonators b, c, d, are interconnected between the initialstructure a and the final structure g. Theinitial 1 structure 02-consists of two masses, the telephone casing 14 together with the fieldmag- 1 net 15and the armature 16, which are connected with one anotherby an elastic-diaphragm 17. Similarly, as in Figure 1 the resonatorshave'common masses so that:

. .Riesonator b embraces; chamber 17 and partly 18.

Resonator cnchamber 18 and partly 19. Resonator d chamber 19 and partly20 A similar device shows Figure 3 in which the mechanical system h of aloud speaker 18 coupled with radiating funnel i by means'ofinterconnected resonance chambers 17 1S 18, 19 19, 20; 20, 21-; 21,22;;these chambers and the openings 23- -27 in the walls be- .tween thechambers bein so adjusted or dimensionedthat a gradua increasing ratioof the masses of neighboring structures exists a and a degree ofcoupling of suchtightness that a good transfer of energy between it andi is obtained. In this case a very tight coupling must be used onaccountof the very broad range of frequencies (speech-and music) desired to bereproduced and therefore the masses have to decrease verv slowlv fromstructure to structure. Therefore it is difiicult to obtain a sufiicienttight coupling be-.

tween the first structure (diaphragm 2 with armature. 3) and thecooperating chamber without intermediatestructures. According to theinvention in this case' one or more coupled mechanical structures withgradual decreasing masses must be inserted between the initial structureandthe first resonance chamber, as it is shown at 28 in Figure 3.

y In all three examples described above (Figure 1-3), all structures,the mechanical ones and the resonator chambers preferably must be tunedsubstantially to the same fre quency. I

It maybe understood that the invention is not limited to the examplesshown in'the figures. The: invention may be applied generally in' alloasesin which. two definite vibratory structures, an initial structureand a final structure are to operate with one" another over a broadrange of frequencies. If this range is excessively broad as for instancefor the human voice and'inusic which include vibrations from the highestto the lowest frequencies according .to the invention a large number ofvibrator-y structures has to be interconnected between the twoend-structures. The closer the coupling between them the better thecondition of a broad resonance diagram can be fulfilled with as fewinterconnectedvibratory structures as possible.

We claim 1. Acoustical vibratory apparatus consisting of a plurality (atleast three) vibratory structures built up of separate masses andconnecting elastic members coupled with one another in series with theaid of their masses and each elastlc member being held at its rim by oneof the said masses and carrying in its middle zone the following mass.

2. Acoustical vibratory apparatus consisting of a plurality (at leastthree) of equally tuned vibratory structures coupled in series withoneanother, the said apparatus comprising an initial vibratory structureand a final vibratory structure of vibratory magnitudes (mass andelastic force) of different value; the value of the vibratory magnitudesof the intermediate structures decreasing gradually in equal stepstowards the struc ture with the smallest vibratory magnitudes.

3. Acoustic vibratory apparatus comprising two end masses and aplurality of intermediatemasses, a plurality of elastic members, eachmass bein coupled to the adj'acentanass'by one of said elastic members,said masses being so adjusted with regard to mag. ni'tudethat theresonance crests of the apparatus are evenl distributed over the rangeof fre ueneies or whichthe apparatusis to be us 4. Acoustic vibratoryapparatus comprising two end masses and a plurality of'intermediate mases, a plurality of elastic members, each mass being coupled to theadjacent mass by one of said elastic members, forming a series ofvibratory structures of masses coupled by elastic members, each of theintermediate masses serving as a coupling mass, said masses being'soproportional with" regard to weights and said structures being so dampedthat the resonance crests of the apparatus are evenly distributed overthe range of frequencies for which the apparatus is to be used and thepeaks are not more than twice the lowest point of the resonance curve.

5. Acoustic vibratory apparatus comprising a casing, a diaphragmsupported by said casing, a mass having a circular flange attached tosaid diaphragm, a second diaphragm mounted on said circular flange, anda plurality of similar structures, each having a. mass and an elasticmember mounted seri- 20 ally on said first elastic member.

6. Acoustic vibratory apparatus comprising a casing, adiaphragrnsupported by said casing, a mass having a circular flange attached tosaid diaphragm, a second diaphragm mounted on said circular flange, and

a plurality of similar structures, each having a mass and an elasticmember mounted serially on said first elastic member, said masses beingproportioned ,to one another in only gradually diminishing steps.

7. Acoustic vibratory apparatus comprising two end masses and aplurality of intermediate masses, said masses being proportioned to oneanother successively in gradually diminishing steps, and a plurality ofelastic members, each mass being coupled to the adjacent mass by one ofsaid elastic members.

In testimony whereof we aflix our signatures.

WALTER HAHNEMANN- HEINRICH HECHT.

